Backrest for a chair



FIG. 1 is a front perspective view of a backrest for a chair showing thenew design;

FIG. 2 is a rear perspective view thereof;

FIG. 3 is a front view;

FIG. 4 is a rear view;

FIG. 5 is a left view;

FIG. 6 is a right view;

FIG. 7 is a top view; and,

FIG. 8 is a bottom view.

CLAIM The ornamental design for a backrest for a chair, as shown anddescribed.